1. Field of the Invention
The present invention relates to a transmitting circuit device used for a transmitting circuit of a wireless communications device as well as to a wireless communications device using it.
2. Related Art of the Invention
Recently, with the spread of cellular phones, cellular phone terminals have grown in functionality. For example, via a basestation, cellular phone terminals can now communicate wirelessly with a remote cellular phone terminal in a higher-quality voice, send and receive e-mail, and download images and programs through the Internet. In addition to growth in functionality, cellular phone terminals have been achieving reductions in size and power consumption.
One factor which has enabled growth in the functionality of cellular phone terminals is the adoption of digital wireless communications methods, such as CDMA, which allow larger amounts of information to be carried without error than do conventional analog wireless communications methods. These wireless communications methods employ QPSK or other similar modulation method and generally use a quadrature modulator as a component of a transmitting circuit device.
FIG. 26 shows a basic configuration of a conventional transmitting circuit device. In the figure, the transmitting circuit device consists of a quadrature modulator 403, bandpass filter 404, IQ signal generator 405, local oscillator 406, and power amplifier 411. The quadrature modulator 403 consists of a phase shifter 407, mixer 408, mixer 409, and combiner 410.
The IQ signal generator 405 outputs a baseband I signal and baseband Q signal—analog signals—which are input in the quadrature modulator 403. The local oscillator 406 outputs a carrier-frequency sine wave signal, which is then divided by the phase shifter 407 into two signals 90 degrees out of phase with each other. The resulting signals are input in the mixer 408 and mixer 409, which then use the baseband I signal and baseband Q signal, respectively, to amplitude-modulate the carrier-frequency signals 90 degrees out of phase with each other. The modulated signals are combined by the combiner 410 as an output of the quadrature modulator 403. The output of the quadrature modulator 403 is amplified by the power amplifier 411 and has unnecessary frequency components reduced by the bandpass filter 404 before it is output.
However, with the conventional transmitting circuit device, since the baseband I signal and baseband Q signal inputted in the quadrature modulator 403 are analog signals, it is necessary to prevent the mixers 408 and 409 from causing distortion. Thus, it is difficult to ensure a sufficiently high level of output from the quadrature modulator 403.
To raise the output of the quadrature modulator 403 to a sufficiently high level, it must be amplified by the power amplifier 411. Since the power amplifier 411 must be operated in a linear region relatively free of distortion, it must operate at a sufficiently low level compared to its saturation level. This causes the power amplifier 411 to consume much power, making it impossible to reduce power consumption of the transmitting circuit device as a whole.
To solve this conventional problem, applicants proposed a transmitting circuit device shown in FIG. 27 in Japanese Patent Laid-Open No. 2002-57732.
The disclosure of Japanese Patent Laid-Open No. 2002-57732 is incorporated herein by reference in its entirety.
FIG. 27 shows a basic configuration of the transmitting circuit device proposed by this applicant in his first patent application. In the figure, the transmitting circuit device consists of a first digital modulator 1001, second digital modulator 1002, quadrature modulator 1003, IQ data generator 1005, and local oscillator 1006.
Moreover, the quadrature modulator 1003 consists of a phase shifter 1007, first digital RF modulator 1008, second digital RF modulator 1009, first bandpass filter 1110, second bandpass filter 1111, and combiner 1010.
Next, operation of this transmitting circuit device will be described.
First, the IQ data generator 1005 outputs a baseband I signal to the first digital modulator 1001, and a baseband Q signal to the second digital modulator 1002. The baseband I signal and baseband Q signal are multilevel digital signals. The first digital modulator 1001 delta-sigma modulates an input signal and outputs a digital I signal which has a lower vertical resolution, i.e., a smaller number of available values than a baseband modulating signal. Similarly, the second digital modulator 1002 delta-sigma modulates an input signal and outputs a digital Q signal.
A local signal outputted by the local oscillator 1006 is divided by the phase shifter 1007 into carrier-frequency signals 90 degrees out of phase with each other. The two carrier-frequency signals are input in the first digital RF modulator 1008 and second digital RF modulator 1009, respectively. The carrier-frequency signal inputted in the first digital RF modulator 1008 is amplitude-modulated stepwise by an output signal from the first digital modulator 1001 while the carrier-frequency signal 90 degrees out of phase inputted in the second digital RF modulator 1009 is amplitude-modulated stepwise by an output signal from the second digital modulator 1002.
Output from the first digital RF modulator 1008 is input in the combiner 1010 through the first bandpass filter 1110 while output from the second digital RF modulator 1009 is input in the combiner 1010 through the second bandpass filter 1111. These inputs are added by the combiner 1010 to produce a transmitter output signal of the quadrature modulator 1003. The first bandpass filter 1110 and second bandpass filter 1111 are installed to reduce unnecessary frequency components which occur in outputs of the first digital RF modulator 1008 and second digital RF modulator 1009, respectively. In the configuration shown in FIG. 27, the bandpass filters 1110 and 1111 can reduce unnecessary frequency components before combining signals.
Since a digital RF modulator needs to output only those levels which exactly correspond to digital IQ signals which have a lower vertical resolution, i.e., a smaller number of available values, it does not need to have high linearity. Thus, elements included in the digital RF modulator can be used at levels close to their saturation levels, resulting in high efficiency. Also, since there are a small number of components dependent on analog characteristics, it is easy to ensure linearity.
Thus, the transmitting circuit device proposed by this applicant in his first patent application solves the above problem and offers great advantages: namely, by delta-sigma modulating the baseband IQ signals into digital IQ signals which has a lower vertical resolution, i.e., a smaller number of available values than the baseband IQ signals and modulating the carrier waves with the quadrature modulator, it can achieve good linearity and low power consumption.
FIG. 28 shows a basic configuration of a transmitting circuit device proposed by this applicant in Japanese Patent Laid-Open No. 2002-325109.
The disclosure of Japanese Patent Laid-Open No. 2002-325109 is incorporated herein by reference in its entirety.
The transmitting circuit device consists of a frequency modulator 1101, amplitude modulator 1102, delta sigma modulator 1103, bandpass filter 1104, and data generator 1105.
The data generator 1105 serves as a means of dividing an incoming digital signal and outputting vector modulation data composed of frequency modulation data and amplitude modulation data, both of which are digital signals that take discrete values.
The frequency modulator 1101 serves as a means of frequency-modulating a carrier-frequency signal using frequency modulation data.
The delta sigma modulator 1103 is a high-order delta sigma modulator and serves as a means of delta-sigma modulating amplitude modulation data and outputting digital amplitude data which has a lower vertical resolution, i.e., a smaller number of available values than the amplitude modulation data.
The amplitude modulator 1102 serves as a means of amplitude-modulating an output signal of the frequency modulator 1101 using the digital amplitude data outputted from the delta sigma modulator 1103.
The bandpass filter 1104 serves as a means of reducing unnecessary frequency components in the amplitude modulator 1102. Whereas the transmitting circuit device shown in FIG. 26 which employs a conventional quadrature modulator needs two bandpass filters, the transmitting circuit device in FIG. 28 needs only one bandpass filter. In this way, the transmitting circuit device in FIG. 28 needs a smaller number of bandpass filters than do conventional transmitting circuit devices.
Next, operation of this transmitting circuit device will be described.
The data generator 1105 generates vector modulation data by dividing an incoming digital signal. Specifically, as the vector modulation data, it generates and outputs frequency modulation data and amplitude modulation data, both of which are digital signals.
The frequency modulator 1101 frequency-modulates a carrier-frequency signal using the frequency modulation data outputted from the data generator 1105. FIG. 29(a) shows a signal which has been frequency-modulated by the frequency modulator 1101. It can be seen that the frequency-modulated signal has a constant envelope.
The delta sigma modulator 1103 is a high-order delta sigma modulator. It delta-sigma modulates amplitude modulation data and outputs digital amplitude data which has a lower vertical resolution, i.e., a smaller number of available values than the amplitude modulation data.
FIG. 29(b) shows amplitude modulation data which is input in the delta sigma modulator 1103. The amplitude modulation data is transmitted to the delta sigma modulator 1103 via a bus line on which data bits are transmitted on respective signal lines in synchronization with a clock signal. FIG. 29(c) shows output data from the delta sigma modulator 1103. In FIG. 29(c), the output data from the delta sigma modulator 1103 is modulated into binary digital amplitude data. Although the amplitude modulation data has been described as data transmitted via a bus line as shown in FIG. 29(b), it may alternatively be transmitted as a multilevel analog signal which takes discrete values.
The amplitude modulator 1102 amplitude-modulates the output signal of the frequency modulator 1101 using digital amplitude data.
Output of the amplitude modulator 1102 has unnecessary frequency components reduced by the bandpass filter 1104.
The output of the frequency modulator 1101 is a frequency-modulated signal and thus, has a constant envelope. The amplitude modulator 1102, which performs amplitude modulation using digital amplitude data, needs to provide only a small number of output levels proportional to the numeric values of the data because the digital amplitude data has a low vertical resolution, i.e., a smaller number of available values. Thus, even an amplitude modulator with low linearity can readily correct output levels.
If the delta sigma modulator 1103 is configured to produce 1-bit outputs, in particular, the amplitude modulator needs to operate simply as a switch. This allows the amplitude modulator 1102 to operate nearly at its saturation level, resulting in high efficiency. Also, since there are a small number of components dependent on analog characteristics, it is possible to obtain good linearity even using elements prone to produce high distortion.
Thus, the transmitting circuit device proposed by this applicant solves the above problem and offers great advantages: namely, it can achieve good linearity, high transmitter output power efficiency, and low power consumption.
Although the frequency modulator 1101 is used in the example described above, this is not restrictive. Instead of the frequency modulator 1101, the transmitting circuit device proposed by this applicant can also use a phase modulator which phase-modulates carrier-frequency signals using the phase modulation data outputted from the data generator 1105. In short, the transmitting circuit device described above can produce the same effect using a frequency modulator or angle modulator such as a phase modulator.
FIG. 30 shows a transmitting circuit device proposed in order to solve the conventional problem described above. This transmitting circuit device amplifies discrete analog signals unlike the transmitting circuit device shown in FIG. 26. It consists of a delta sigma modulator 1202, amplifier 1203, and bandpass filter 1204.
The delta sigma modulator 1202 delta-sigma modulates input data received via an input terminal 1201 and outputs digital data which has a lower vertical resolution, i.e., a smaller number of available values than the input data.
The digital data outputted from the delta sigma modulator 1202 goes through D/A conversion, is amplified by the amplifier 1203, passes through the bandpass filter 1204 to reduce unnecessary frequency components including quantization noise produced when the input data is quantized by the delta sigma modulator 1202, and is output through an output terminal 1205.
Since the delta sigma modulator 1202 converts the input data into digital data which has a lower vertical resolution, i.e., a smaller number of available values, the amplifier 1203 needs to output only those levels which exactly correspond to the digital data which has a lower vertical resolution, i.e., a smaller number of available values and does not need to have high linearity. Thus, elements included in the amplifier 1203 can be used at levels close to their saturation levels, resulting in high efficiency. Also, since there are a small number of components dependent on analog characteristics, it is easy to ensure linearity.
However, with any of the transmitting circuit devices shown in FIGS. 27, 28, and 30, quantization noise occurs when the input signal to the delta sigma modulator is delta-sigma modulated. To reduce the quantization noise, it is necessary to use a bandpass filter with steep characteristics.
A bandpass filter with steep characteristics has a large size, which increases the circuit scale of the transmitting circuit device accordingly. Also, a bandpass filter with steep characteristics involves high losses, decreasing the efficiency of the transmitting circuit device itself.
Thus, the proposed transmitting circuit devices have the problem of increased size resulting from the large size of the bandpass filter.
Also, the proposed transmitting circuit devices have the problem of lowered efficiency resulting from the high losses of the bandpass filter.
In view of the above problems, the present invention has an object to provide a transmitting circuit device and wireless communications device small in size.
Also, in view of the above problems, the present invention has an object to provide a transmitting circuit device and wireless communications device which have high efficiency.